HK1207483B

HK1207483B - Acoustic wave device and antenna duplexer using the same

Info

Publication number: HK1207483B
Application number: HK15107943.6A
Authority: HK
Inventors: 岩崎智弘; 中村弘幸; 小松祯也
Original assignee: 天工滤波方案日本有限公司
Priority date: 2012-07-30
Filing date: 2013-07-26
Publication date: 2018-03-16

Description

Elastic wave device and antenna duplexer using the same

Technical Field

The present invention relates to an elastic wave device and an antenna duplexer using the same.

Background

Fig. 10 is a schematic cross-sectional view of a conventional elastic wave device 101. The elastic wave device 101 includes a piezoelectric substrate 102, comb-shaped electrodes 103 formed on the piezoelectric substrate 102 and configured to excite Rayleigh waves (Rayleigh waves) of a wavelength λ as main elastic waves, and a dielectric film 104 formed above the substrate 102 so as to cover the comb-shaped electrodes 103.

The dielectric film 104 having a Temperature Coefficient of Frequency (TCF) of opposite sign to that of the piezoelectric substrate 102 improves the TCF of the elastic wave device 101.

A conventional elastic wave device similar to the elastic wave device 101 is disclosed in, for example, patent document 1.

The conventional elastic wave device 101 generates an unwanted elastic wave, i.e., a shear-horizontal (SH) wave, having a frequency between the resonance frequency and the antiresonance frequency of the rayleigh wave, which is a main elastic wave. In the case where the elastic wave device 101 is used in a ladder filter or a dual-mode saw (dms) filter, the SH wave generates ripples (ripples) in the pass band of these filters and causes deterioration of the characteristics thereof.

Fig. 11 shows the admittance characteristics (dB) of the elastic wave device 101. In the elastic wave device 101, the piezoelectric substrate 102 is made of lithium niobate (LiNbO)₃) A base plate having a cut plane expressed by Euler angles (phi, theta, phi) and a Rayleigh wave propagation direction, wherein-10 DEG-phi 10 DEG, 33 DEG-theta 43 DEG, and-10 DEG-phi 10 deg. The comb-shaped electrode 103 is made of a molybdenum electrode having a film thickness of 0.05 λ, and a rayleigh wave having an excitation wavelength λ of 4000nm is taken as a main elastic wave. The dielectric film 104 is made of silicon dioxide having a film thickness of 0.25 λ, which is measured from the interface between the substrate 102 and the dielectric film 104 to the upper surface of the dielectric film 104. As shown in fig. 11, spurious emissions (spurious emissions) 108 are generated from an SH wave, which is an unnecessary elastic wave, between the resonance point and the antiresonance point of the rayleigh wave.

Prior art documents

Patent document

Patent document 1: international publication No. WO2005/034347

Disclosure of Invention

An elastic wave device includes: a piezoelectric substrate; a comb-shaped electrode that is formed on the piezoelectric substrate and excites Rayleigh waves as main elastic waves; a first dielectric film formed on the piezoelectric substrate so as to cover the comb-shaped electrode; and a second dielectric film having a part thereof disposed between the electrode fingers of the comb-shaped electrode and a part thereof disposed above the comb-shaped electrode. The portion of the second dielectric film disposed between the electrode fingers of the comb-shaped electrode is disposed between the piezoelectric substrate and the first dielectric film. A portion of the second dielectric film disposed above the comb-shaped electrode is disposed between the comb-shaped electrode and the first dielectric film. The velocity of the transverse wave propagating through the first dielectric film is lower than the velocity of the rayleigh wave excited by the comb-shaped electrode. The velocity of the transverse wave propagating through the second dielectric film is higher than the velocity of the rayleigh wave excited by the comb-shaped electrode.

This structure prevents the increase in the frequency of the rayleigh wave, which is the main elastic wave, while relatively increasing the frequency of the SH wave, which is an unnecessary elastic wave. While the energy of both the SH wave and the rayleigh wave is concentrated near the upper surface of the piezoelectric substrate, the energy of the rayleigh wave is distributed in the first dielectric film more largely than the SH wave, so that the increase in the frequency of the rayleigh wave can be prevented.

As a result, in the filter using the elastic wave device, spurious emissions caused by the SH wave are removed from the passband of the filter, and thus the pass characteristic of the filter is improved.

Drawings

Fig. 1 is a schematic cross-sectional view of an elastic wave device according to an exemplary embodiment of the present invention.

Fig. 2 shows characteristics of an elastic wave device according to the embodiment.

Fig. 3 shows characteristics of an elastic wave device according to the embodiment.

Fig. 4 is a schematic cross-sectional view of another elastic wave device according to an embodiment.

Fig. 5 shows characteristics of an elastic wave device according to the embodiment.

Fig. 6 is a schematic cross-sectional view of yet another elastic wave device according to an embodiment.

Fig. 7 is a schematic cross-sectional view of still another elastic wave device according to an embodiment.

Fig. 8A illustrates characteristics of an elastic wave device according to an embodiment.

Fig. 8B illustrates characteristics of an elastic wave device according to the embodiment.

Fig. 8C shows characteristics of the elastic wave device according to the embodiment.

Fig. 9 is a circuit block diagram of an antenna duplexer including an elastic wave device according to an embodiment.

Fig. 10 is a schematic cross-sectional view of a conventional elastic wave device.

Fig. 11 shows characteristics of a conventional elastic wave device.

Detailed Description

Fig. 1 is a schematic cross-sectional view of an elastic wave device according to an exemplary embodiment of the present invention (a schematic cross-sectional view perpendicular to an extending direction of an interdigital transducer (IDT) electrode).

An elastic wave device 1 shown in fig. 1 includes a piezoelectric substrate 2, comb-shaped electrodes 3 formed on the piezoelectric substrate 2 and exciting rayleigh waves as main elastic waves, and a first dielectric film 4 formed on the substrate 2 so as to cover the comb-shaped electrodes 3. The acoustic wave device 1 further includes a second dielectric film 5 disposed between the electrode fingers of the comb-shaped electrodes 3 and between the piezoelectric substrate 2 and the first dielectric film 4, and a second dielectric film 6 disposed above the comb-shaped electrodes 3 and between the comb-shaped electrodes 3 and the first dielectric film 4. The wavelength λ of the rayleigh wave is 2 times as long as the pitch of the electrode fingers.

The velocity of the transverse wave propagating through the first dielectric film 4 is lower than the velocity of the rayleigh wave excited by the comb-shaped electrode 3. The velocity of the transverse wave propagating through the second dielectric films 5 and 6 is higher than the velocity of the rayleigh wave excited by the comb-shaped electrode 3.

The velocity of a horizontal Shear (SH) wave excited by the comb-shaped electrode 3 as an unwanted elastic wave is higher than the velocity of a transverse wave propagating through the first dielectric film 4 and lower than the velocity of a transverse wave propagating through the second dielectric films 5 and 6.

Without providing the second dielectric films 5 and 6, an unnecessary elastic wave, i.e., SH wave, is generated between the resonance frequency and the antiresonance frequency of the main elastic wave, i.e., rayleigh wave.

The elastic wave device 1 relatively increases the frequency of SH wave, which is an unnecessary elastic wave, while preventing an increase in the frequency of rayleigh wave. Since the energy of both the SH wave and the rayleigh wave is concentrated near the upper surface of the piezoelectric substrate 2, and the energy of the rayleigh wave is distributed in the first dielectric film 4 more than the SH wave, the increase in the frequency of the rayleigh wave is prevented.

As a result, spurious emissions caused by SH waves are removed from the pass band of the filter when the acoustic wave device 1 is used in the filter, thereby improving the pass characteristics of the filter.

The piezoelectric substrate 2 is made of a piezoelectric single crystal substrate that excites rayleigh waves as main elastic waves. For example, the piezoelectric substrate 2 is made of lithium niobate (LiNbO)₃) Is made of a base plate having a cut angle expressed by Euler angles (phi, theta, phi) and a Rayleigh wave propagation direction, wherein-10 DEG-phi 10 DEG, 33 DEG-theta 43 DEG, and-10 DEG-phi 10 deg. The piezoelectric substrate 2 may be a piezoelectric medium (medium) substrate or a piezoelectric medium film, for example, made of a quartz substrate or lithium tantalate (LiTaO)₃) Is made of a base substrate, a potassium niobate base substrate, or a piezoelectric single crystal medium. The piezoelectric substrate 2 made of a quartz-based substrate has a cut angle expressed by Euler angles (phi, theta, phi) and a main elastic wave propagation direction, wherein-1 DEG or more phi or less 1 DEG, 113 DEG or more theta or less 135 DEG, and-5 DEG or more phi or less 5 deg. From lithium tantalate (LiTaO)₃) The piezoelectric substrate 2 made of a silicon substrate has a cut angle expressed by Euler angles (phi, theta, phi) and a main elastic wave propagation direction, wherein-7.5 DEG or more phi or less 2.5 DEG, 111 DEG or more theta or less 121 DEG, and-2.5 DEG or more phi or less 7.5 deg. Angles Φ and θ represent cut angles of the piezoelectric substrate 2, and angle ψ represents a propagation direction of a main elastic wave excited by the comb-shaped electrode 3 formed on the piezoelectric substrate 2.

The comb-shaped electrodes 3 provided on the piezoelectric substrate 2 include a pair of interdigital transducers having comb shapes that cross each other when viewed from above the elastic wave device 1. The comb-shaped electrode 3 is made of a single metal such as aluminum, copper, silver, gold, titanium, tungsten, molybdenum, platinum, or chromium, an alloy mainly containing one of these metals, or a laminated structure of these metals. In the case where the comb-shaped electrode 3 has a laminated structure, for example, the comb-shaped electrode 3 includes a Mo electrode layer mainly made of molybdenum and an Al electrode layer mainly made of aluminum and disposed on the Mo electrode layer in order from the piezoelectric substrate 2. The Mo electrode layer has a higher density, and therefore confines a main elastic wave on the surface of the elastic wave device 1, whereas the Al electrode layer reduces the resistance of the comb-shaped electrode 3. The Mo electrode layer may contain additives such as silicon, while the Al electrode layer may contain additives such as magnesium, copper, or silicon. These additives increase the withstand voltage of the comb electrode 3.

The total film thickness of the comb-shaped electrode 3 is expressed by the total density "b" of the comb-shaped electrode 3 and the density "a" of aluminum, and is preferably not less than 0.05 λ × b/a and not more than 0.15 λ × b/a. This condition allows the main elastic wave to be concentrated on the surface of the elastic wave device 1.

The first dielectric film 4 may be made of any medium through which the velocity of the cross wave propagating is lower than the rayleigh wave excited by the comb-shaped electrode 3. For example, the first dielectric film 4 is made of mainly silicon dioxide (SiO)₂) The finished media. SiO 2₂Has a frequency Temperature Coefficient (TCF) of opposite sign to that of the piezoelectric substrate 2. From SiO₂The first dielectric film 4 is formed to improve the frequency temperature coefficient of the acoustic wave device 1.

In the case where the first dielectric film 4 is made of silicon oxide, the film thickness of the first dielectric film 4 is determined such that the absolute value of the frequency-temperature coefficient of the main elastic wave excited by the comb-shaped electrode 3 is not more than a predetermined value (40ppm/° c). According to this embodiment, the film thickness of the first dielectric film 4 is the distance from the interface between the first dielectric film 4 and the second dielectric film 5 provided between the electrode fingers of the comb-shaped electrode 3 to the upper surface of the first dielectric film 4. The thickness of the first dielectric film 4 that satisfies the predetermined value and is made of silicon oxide is not less than 0.2 λ and not more than 0.5 λ.

The second dielectric films 5 and 6 may be made of any medium through which the velocity of the cross wave propagating is faster than the rayleigh wave excited by the comb-shaped electrode 3. The medium may be made mainly of, for example, diamond, silicon nitride, silicon oxynitride, aluminum nitride, or aluminum oxide.

Fig. 2 shows the admittance characteristics (dB) of the elastic wave device 1 including the piezoelectric substrate 2, the comb-shaped electrode 3, the first dielectric film 4, and the second dielectric films 5 and 6. The piezoelectric substrate 2 is made of lithium niobate (LiNbO)₃) The base plate is made to have a cut angle expressed by Euler angles (phi, theta, phi) and a Rayleigh wave propagation direction, wherein phi is-10 DEG or more and 10 DEG or less, theta is 33 DEG or more and 43 DEG or less, and phi is-10 DEG or more and 10 DEG or less. The comb-shaped electrode 3 includes a molybdenum electrode having a film thickness of 0.05 λ and a rayleigh wave having an excitation wavelength λ of 4000nm as a main elastic wave. The first dielectric film 4 is made of silicon dioxide (SiO)₂) As a result, the film thickness measured from the interface between the second dielectric film 5 and the first dielectric film 4 to the upper surface of the film 4 was 0.25 λ. The second dielectric films 5 and 6 are made of silicon nitride (SiN), and the film thickness thereof is 0.045 λ.

As shown in fig. 2, the second dielectric films 5 and 6 move spurious emissions 8 (at the resonance point of the SH wave) generated by the SH wave to a higher frequency than the anti-resonance point 7 of the rayleigh wave.

Fig. 3 shows the frequency change of spurious emissions generated by the SH wave for a change in the film thickness (d) of the second dielectric films 5 and 6 from 0 λ to 0.0125 λ. Each frequency change is a percentage calculated by dividing the change by the resonance frequency of the SH wave, and is expressed with reference to the film thickness (d) of the second dielectric films 5 and 6.

As shown in fig. 2 and 3, the larger film thickness of the second dielectric films 5 and 6 more effectively prevents the frequency of the rayleigh wave (i.e., the primary elastic wave) from increasing while relatively increasing the frequency of the SH wave (i.e., the unnecessary elastic wave). Since the energy of both the SH wave and the rayleigh wave is concentrated near the upper surface of the piezoelectric substrate 2, and the energy of the rayleigh wave is distributed in the first dielectric film 4 more than the SH wave, the increase in the frequency of the rayleigh wave is prevented.

As a result, spurious emissions caused by SH waves are removed from the pass band of the filter when the acoustic wave device 1 is used in the filter, and thus the pass characteristic of the filter is improved.

As shown in fig. 4, the film thickness of the second dielectric film 6 formed above the comb-shaped electrodes 3 is preferably smaller than the film thickness of the second dielectric film 5 formed between the electrode fingers of the comb-shaped electrodes 3.

Fig. 5 shows that the frequency of spurious emissions caused by SH waves changes for a change in the film thickness of the second dielectric film 6 from 0.0125 λ to 0 λ when the film thickness (d) of the second dielectric film 5 is kept at 0.0125 λ. Each frequency change is a percentage calculated by dividing the change by the resonance frequency of the SH wave, and is expressed with reference to the film thickness (d) of the second dielectric film 6 of 0.0125 λ. The piezoelectric substrate 2 is made of lithium niobate (LiNbO)₃) Is made of a base plate having a cut angle expressed by Euler angles (phi, theta, phi) and a Rayleigh wave propagation direction, wherein-10 DEG-phi 10 DEG, 33 DEG-theta 43 DEG, and-10 DEG-phi 10 deg. The comb-shaped electrode 3 includes a molybdenum electrode layer having a film thickness of 0.05 λ and a rayleigh wave having an excitation wavelength λ of 4000nm as a main elastic wave. From silicon dioxide (SiO)₂) The first dielectric film 4 was formed to have a film thickness of 0.25 λ. The second dielectric films 5 and 6 are made of silicon nitride (SiN).

The film thickness of 0 λ of the second dielectric film 6 refers to a structure in which the second dielectric film 6 is not formed above the comb-shaped electrodes 3, that is, the upper surfaces of the comb-shaped electrodes 3 directly contact the first dielectric film 4, as shown in fig. 6. More specifically, the elastic wave device 1 shown in fig. 6 includes a piezoelectric substrate 2, comb-shaped electrodes 3 that are formed on the piezoelectric substrate 2 and excite rayleigh waves as main elastic waves, a first dielectric film 4 that is formed above the substrate 2 so as to cover the comb-shaped electrodes 3, and a second dielectric film 5 that is formed between electrode fingers of the comb-shaped electrodes 3 and between the piezoelectric substrate 2 and the first dielectric film 4.

As shown in fig. 5, the second dielectric film 6 formed above the comb-shaped electrodes and having a smaller film thickness than the second dielectric film 5 formed between the electrode fingers of the comb-shaped electrodes 3 more effectively prevents the frequency of the rayleigh wave, which is the main elastic wave, from increasing while relatively increasing the frequency of the SH wave, which is the unnecessary elastic wave. In the vicinity of the upper surface of the piezoelectric substrate 2, the SH wave generates energy larger than the rayleigh wave, and is therefore affected by the additional mass of the second dielectric film 6 provided above the comb-shaped electrode 3. Therefore, the second dielectric film 6 formed above the comb-shaped electrodes 3 is thinner than the second dielectric film 5 formed between the electrode fingers of the comb-shaped electrodes 3 to further increase the frequency of the SH wave.

As a result, the acoustic wave device 1, when used in a filter, removes spurious emissions caused by SH waves from the pass band of the filter, thereby improving the pass characteristics of the filter.

As shown in fig. 7, the second dielectric films 5 and 6 may preferably be formed on the side surfaces of the electrode fingers of the comb-shaped electrode 3. This structure allows the dielectric films 5 and 6 to protect the comb-shaped electrode 3 more.

In the acoustic wave device 1 shown in fig. 1, 4, and 6, the film thickness of the second dielectric film 5 formed between the electrode fingers of the comb-shaped electrode 3 is smaller than the film thickness of the comb-shaped electrode 3. This structure ensures the electromechanical coupling coefficient.

Fig. 8A to 8C show the electromechanical coupling coefficient of the elastic wave device 1 in which the film thickness of the second dielectric 5 made of silicon nitride (the same as the film thickness of the second dielectric film 6) is changed. In the elastic wave device 1, the piezoelectric substrate 2 is made of lithium niobate (LiNbO)₃) Is made of a substrate. The comb-shaped electrode 3 includes a molybdenum electrode layer having a film thickness of 0.05 λ and a rayleigh wave having an excitation wavelength λ of 4000nm as a main elastic wave. The first dielectric film 4 is made of silicon oxide, and its film thickness is 0.25 λ. The second dielectric films 5 and 6 are made of silicon nitride. In fig. 8A to 8C, the horizontal axis represents the ratio of the film thickness of the second dielectric film 5 to the film thickness of the comb-shaped electrode 3, and the vertical axis represents the elastic waveElectromechanical coupling coefficient (%) of the device 1. Fig. 8A shows the electromechanical coupling coefficient of a device in which the piezoelectric substrate 2 is made of a lithium niobate-based substrate having a cut angle and a rayleigh wave propagation direction expressed by euler angles (Φ, θ, ψ) (0 °, 36 °, 0 °). Fig. 8B shows the electromechanical coupling coefficient of a device in which the piezoelectric substrate 2 is made of a lithium niobate-based substrate having a cut angle and a rayleigh wave propagation direction expressed by euler angles (Φ, θ, ψ) (0 °, 38 °, 0 °). Fig. 8C shows the electromechanical coupling coefficient of a device in which the piezoelectric substrate 2 is made of a lithium niobate-based substrate having a cut angle and a rayleigh wave propagation direction expressed by euler angles (Φ, θ, ψ) (0 °, 40 °, 0 °). As shown in fig. 8A to 8C, the piezoelectric substrate 2 is made of lithium niobate (LiNbO) having a cut angle expressed by euler angles (Φ, θ, ψ) and a rayleigh wave propagation direction₃) Is made of a substrate in which-10 DEG.phi.phi.10 DEG, 33 DEG.theta.43 DEG, 10 DEG.phi.phi.phi.phi.phi.phi.phi.phi.10 DEG, and 10 DEG.phi.phi.phi.phi.phi.phi.10 DEG, and 10 DEG, and in the case where the first dielectric film 4 is made of silicon oxide and the film thickness thereof is not less than 0.2 lambda and not more than 0.5 lambda, the film thickness of the second dielectric film 5 formed between the electrode fingers of²Not less than 5%.

Fig. 9 is a circuit block diagram of the antenna duplexer 10 employing the elastic wave device according to the embodiment. As shown in fig. 9, the antenna duplexer 10 includes a first filter 11 having a first pass band and a second filter 12 having a second pass band higher than the first pass band.

The antenna duplexer 10 shown in fig. 9 is for a frequency band 8 of a Universal Mobile Telecommunications System (UMTS), and includes a first filter 11 serving as a transmission filter and a second filter 12 serving as a reception filter. The first filter 11 has a passband from 880MHz to 915MHz and the second filter 12 has a passband from 925MHz to 960 MHz. The first filter 11 is connected between the input terminal 14 and the antenna terminal 15, and receives a transmission signal at the input terminal 14 and outputs the transmission signal from the antenna terminal 15. The first filter 11 includes a series resonator 13 and a parallel resonator 17 connected in a ladder shape. The resonance frequency of the parallel resonator 17 is lower than the anti-resonance frequency of the series resonator 13. The parallel resonator 17 is connected to the ground 20 via a ground terminal 19. The first filter 11 comprises an inductor 18 connected between a ground terminal 19 and ground 20.

The second filter 12 includes, for example, a resonator 21 and a longitudinal-mode coupling filter 22, both of which are connected between the antenna terminal 15 and the output terminal (balanced terminal) 16. The second filter 12 receives the reception signal at the antenna terminal 15 and outputs the reception signal from the output terminal 16.

The antenna duplexer 10 includes a phase shifter 23 connected between the first filter 11 and the second filter 12. The phase shifter 23 provides one of the transmit filter and the receive filter with a high impedance at the pass band of the other of the transmit filter and the receive filter to improve isolation between the transmit filter and the receive filter.

The first filter 11 employs the elastic wave device 1 according to the embodiment. In particular, in the case where the first filter 11 employs a ladder type elastic wave filter, the elastic wave device 1 according to the embodiment at least in the series resonator 13 forming the right wing of the pass band removes spurious emissions caused by SH waves from the pass band of the first filter 11, thereby improving the pass characteristic of the first filter 11.

Industrial applicability

The elastic wave device and the antenna duplexer using the elastic wave device according to the present invention prevent deterioration of the pass characteristic of the filter using the elastic wave device, and are applicable to electronic equipment such as a portable telephone.

Reference numerals

1 elastic wave device

2 piezoelectric substrate

3 comb-shaped electrode

4 first dielectric film

5. 6 second dielectric film

7 antiresonance point

8 spurious emissions caused by SH waves

10 antenna duplexer

11 first filter

12 second filter

13 series resonator

Claims

1. An elastic wave device comprising:

a piezoelectric substrate;

a comb-shaped electrode provided on the piezoelectric substrate and configured to excite a Rayleigh wave as a main elastic wave;

a first dielectric film that is provided above the piezoelectric substrate, covers the comb-shaped electrode, and contacts a side surface of an electrode finger of the comb-shaped electrode, and a velocity of a transverse wave propagating through the first dielectric film is lower than a velocity of a rayleigh wave excited by the comb-shaped electrode; and

a second dielectric film including a first part disposed between electrode fingers of the comb-shaped electrode and between the piezoelectric substrate and the first dielectric film, and a second part disposed above the comb-shaped electrode and between the comb-shaped electrode and the first dielectric film, a velocity of a cross wave propagating through the second dielectric film being higher than a velocity of a rayleigh wave excited by the comb-shaped electrode.

2. The elastic wave device according to claim 1, wherein a film thickness of the second part of the second dielectric film is smaller than a film thickness of the first part of the second dielectric film.

3. The elastic wave device according to claim 1, wherein a film thickness of the first portion of the second dielectric film is smaller than a film thickness of the comb-shaped electrode.

4. The elastic wave device according to claim 1, wherein a velocity of a horizontal shear wave excited by the comb-shaped electrodes is higher than a velocity of a lateral wave propagating through the first dielectric film and lower than a velocity of a lateral wave propagating through the second dielectric film.

5. The elastic wave device according to claim 1, wherein a sign of a frequency temperature coefficient of the first dielectric film is opposite to a sign of a frequency temperature coefficient of the piezoelectric substrate.

6. An antenna duplexer comprising:

a first filter comprising the elastic wave device of claim 1 and having a first pass band; and

a second filter having a second passband higher than the first passband.

7. An elastic wave device comprising:

a piezoelectric substrate;

a second dielectric film including a first portion disposed between the electrode fingers of the comb-shaped electrode and between the piezoelectric substrate and the first dielectric film, a velocity of a transverse wave propagating through the second dielectric film being higher than a velocity of a rayleigh wave excited by the comb-shaped electrode.

8. The elastic wave device according to claim 7, wherein a film thickness of the second dielectric film is smaller than a film thickness of the comb-shaped electrode.

9. The elastic wave device according to claim 7, wherein a velocity of a horizontal shear wave excited by the comb-shaped electrodes is higher than a velocity of a lateral wave propagating through the first dielectric film and lower than a velocity of a lateral wave propagating through the second dielectric film.

10. The elastic wave device according to claim 7, wherein the second dielectric film contacts side surfaces of electrode fingers of the comb-shaped electrode.

11. The elastic wave device according to claim 7, wherein a sign of a frequency temperature coefficient of the first dielectric film is opposite to a sign of a frequency temperature coefficient of the piezoelectric substrate.

12. The elastic wave device according to claim 7, wherein the second dielectric film includes second portions provided on upper surfaces of electrode fingers of the comb-shaped electrode.

13. The elastic wave device of claim 12, wherein the second portion of the second dielectric film is thinner than the first portion of the second dielectric film.

14. The elastic wave device according to claim 7, wherein the first dielectric film contacts upper surfaces of electrode fingers of the comb-shaped electrode.

15. An antenna duplexer comprising:

a first filter comprising the elastic wave device of claim 7 and having a first pass band; and

a second filter having a second passband higher than the first passband.

16. An elastic wave device comprising:

a piezoelectric substrate;

a comb-shaped electrode provided on the piezoelectric substrate and configured to excite a rayleigh wave having a wavelength λ as a main elastic wave;

a first dielectric film that is provided above the piezoelectric substrate and covers the comb-shaped electrode, a velocity of a transverse wave propagating through the first dielectric film being lower than a velocity of a rayleigh wave excited by the comb-shaped electrode; and

a second dielectric film including a first part disposed between electrode fingers of the comb-shaped electrode and between the piezoelectric substrate and the first dielectric film, and a second part disposed above the comb-shaped electrode and between the comb-shaped electrode and the first dielectric film, a velocity of a cross wave propagating through the second dielectric film being higher than a velocity of a rayleigh wave excited by the comb-shaped electrode, a film thickness of the first part of the second dielectric film being larger than a film thickness of the second part of the second dielectric film and smaller than a thickness of the comb-shaped electrode.

17. The elastic wave device of claim 16, wherein the thickness of the first dielectric film is between 0.2 λ and 0.5 λ.

18. The elastic wave device of claim 17, wherein the first dielectric film comprises silicon dioxide.

19. The elastic wave device according to claim 16, wherein a film thickness of the first portion of the second dielectric film is less than 0.9 times a thickness of the comb-shaped electrode.

20. The elastic wave device according to claim 16, wherein the first part of the second dielectric film contacts a side face of an electrode finger of the comb-shaped electrode.